This invention relates to timers of the type advanced in a step-by-step manner by a drive mechanism and, more particularly, to the drive mechanism itself.
When designing a drive mechanism for a switching device in a program timer, a number of criteria must be taken into consideration. For example, it is desirable to advance the switching device at a relatively rapid rate for fast switching action. Prior designs have resulted in an indexing mechanism which drives the switching device in a step-by-step manner by providing a ratchet track on the switching device and a drive pawl which cooperates with the ratchet track to index the switching device. However, these designs have not proven to be entirely satisfactory for a number of reasons. For example, the movement profile of the drive pawl has generally been limited to a sinusoidal motion. Also, these mechanisms have required a relatively large number of parts, increasing the cost of production.
It is therefore an object of this invention to provide a drive mechanism for advancing the switching device in a program timer in a step-by-step manner wherein the movement profile of the drive pawl can be tailored as desired.
It is another object of this invention to provide such a mechanism which comprises a relatively small number of parts.